烯丙氧羰基（Alloc）同前面提到的Cbz、Boc和Fmoc不同，它对酸、碱等都很稳定，在它的存在下，Cbz、Boc和Fmoc等可选择性去保护，而它的脱去则通常在Pd(0)的存在下进行。

烯丙氧羰基（Alloc）的引入

Alloc-Cl在有机溶剂/Na₂CO₃、NaHCO₃溶液或吡啶中同氨基化合物反应则可得到Aloc保护的氨基衍生物【 E. J. Corey, J. W. Suggs., J. Org. Chem., 1973,38, 3223】

反应实例

To a stirred solution of compound 1 (3.0 g, 15.86 mmol) in a mixture of aq. NaHCO₃andTHF (8/2, 20 mL) was added allylchloro formate (2.54 mL, 23.81 mmol), dropwiseand at 0 °C. Themixture was stirred at room temperature for 12 h and then diluted with ethylacetate and washed 3 N HCl, dried and the solvent removed in vacuo togive compound 2 as a pale yellow oil, which was used without further purification(3.55 g, 82%).

【Micale, Nicola;Vairagounder, Rajendran et al J. Med. Chem., 2004, 47(26),6455-6458】

To a solution of 17 (1.0 g, 1.97 mmol) in EtOAc (10 ml) was added 4 M HCl/EtOAc (20 mL), and the mixture was stirredfor 6 h at room temperature. After evaporation, to the suspension of theresidue in CH₂Cl₂(40 mL) were added triethylamine (2.75 mL,19.7 mmol) and allyl chloroformate (0.627 mL, 5.91 mmol) at -10°C.The reaction mixture was poured into H₂O and the whole was extracted withEtOAc. The organic layer was washed with brine, dried over MgSO₄, andevaporated under reduced pressure. The residue was purified by silica gelcolumn chromatography (EtOAc/acetone = 8:1) to give 18 (863 mg, 92.1%)as a foam. [ a]_D²⁵=19.6 (c =1.0,CHCl₃).

【H. Imamura; A.Shimizu et al., Tetrahedron, 2000, 56(39), 7705】

烯丙氧羰基（Alloc）的脱去

Alloc保护基对酸、碱等较强的稳定性，它们通常只用Pd(0)，如Pd(PPh₃)₄或Pd(PPh₃)₂Cl₂存在的条件去保护。例如，Alloc衍生物用Pd(PPh₃)₄/Me₂NTMS处理，可以得到易水解的氨基甲酸TMS酯 ^{[TetrahedronLett., 1992, 33,477]}。脱去含硫衍生物中的Alloc 时，如蛋氨酸，Pd(PPh₃)₄/二甲基环己二酮/TH则不会被毒化^{[Angew.Chem. Int. Ed. Engl., 1984, 23, 436]}。如果在酸性条件下脱除Alloc，则最好采用Pd(PPh₃)₂Cl₂/Bu₃SnH/p-NO₂C₆H₄OH/CH₂Cl₂^{[TetrahedronLett., 1982, 23,1825]}。在异戊烯酯或肉桂酸酯存在下，可用Pd(OAc)₂/TPPT/CH₃CN/Et₃N/H₂O去保护，但随时间的增加，这些酯也会反应，并且氨基甲酸异戊烯酯和烯丙基碳酸酯同样被断裂^{[TetrahedronLett., 1997, 38,2955]}。当加入Boc₂O、AcCl、TsCl、或丁二酸酐时，Pd(PPh₃)₂Cl₂/Bu₃SnH可将Alloc基转变为其它的胺衍生物。另外，Alloc也可在Pd(PPh₃)₄/HCOOH/TEA^{[J.Med. Chem., 1992, 35, 2781]}或AcOH/NMO催化脱去^{[J.Org. Chem., 1996, 61, 3983]}。

反应实例

To a solution of the Allocprotected ester (140.7 mg, 0.2.23mmol)and 1,3-dimethylbarbituric acid (228 mg, 1.46 mmol) in THF (15 mL) was addedtetrakis(triphenylphosphine)palladium (43.9 mg, 0.0379mmol,17 mol%), and the resulting mixture was stirred at rt for 27 h. The mixture wasthen poured into saturated aq. NaHCO₃and extracted fourtimes with Et₂O. The combined extract was dried (MgSO₄)and concentrated in vacuo. The residue was purifiedby chromatography (CHCl₃/MeOH, 20 : 1 to 2 : 1) to give the corresponding freeamino ester as a colorless oil (79.5 mg, 65%).

【Y. Matsushima;H. Itoh etal., J. Chem. Soc. Perkin Trans. 1., 2004, 7,949】

To asolution of 112 (0.97 g,1.4 mmol) in CH₂Cl₂ (19 mL) were added dimethylamino- trimethylsilane(1.32 mL, 8.4 mol) and trimethylsilyl trifluoroacetate (1.45 mL, 8.4 mmol). Thesolution was stirred at 20 °Cfor 10 min, and then Pd(PPh₃)₄(97 mg, 0.084mmol) was added and stirring was continued for 2.5 h. The mixture wasevaporated and the residual oil was dissolved in EtOAc (50 mL). The solutionwas washed with 10% aq NaHCO₃and brine,dried, and evaporated. The residue was chromatographed (SiO₂; EtOAc/hexane 1:2)to give 113 (0.67 g, 78%):foam; TLC Rf) 0.27 (EtOAc).

【P. Angehrm; S.Buchmann et al., J. Med. Chem., 1992, 47(6), 1487】

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